Spinal stenosis typically occurs when the spinal cord, cauda equina and/or nerve root(s) are impinged by one or more tissues in the spine, such as a buckled or thickened ligamentum flavum. Impingement of neural and/or neurovascular tissue in the spine by a buckled or thickened ligamentum flavum may cause pain, numbness and/or loss of strength or mobility in one or both of a patient's lower limbs and/or of the patient's back.
In lumbar spinal stenosis (LSS), space around the spinal cord becomes narrow, thus compressing the spinal cord and the nerve roots. This causes back pain with neurogenic claudication, i.e., pain, numbness, or weakness in the legs that worsens with standing or walking and is alleviated with sitting or leaning forward. Compression of neural elements generally occurs as a result of ligamentum flavum hypertrophy. LSS is one of the most common reasons for back surgery and the most common reason for lumbar spine surgery in adults over 65 years of age. Patients suffering from spinal stenosis are typically first treated with conservative approaches such as exercise therapy, analgesics, anti-inflammatory medications, and epidural steroid injections. When these conservative treatment options fail and symptoms are severe, surgery may be required to remove impinging tissue and decompress the impinged nerve tissue.
Decompressive laminectomy, a well-known treatment for LSS, unroofs the spinal canal by resectioning posterior spinal elements, such as the ligamentum flavum. Wide muscular dissection and retraction is needed to achieve adequate surgical visualization. The extensive resection and injury to the posterior spine and supporting muscles can lead to instability with significant morbidity, both post-operatively and longer-term. Spinal fusion may be required to reduce the resultant instability. Laminectomy may be used for extensive multi-level decompression.
A combination of hemilaminotomy and laminotomy, often referred to as laminoforaminotomy, is less invasive than laminectomy. This procedure focuses on the interlaminar space in order to minimize resectioning of the stabilizing posterior spine. Generally, laminotomy removes the ligamentum flavuum. Muscular dissection and retraction are required to achieve adequate surgical visualization.
Microendoscopic decompressive laminotomy (MEDL) is somewhat similar to laminotomy, but utilizes endoscopic visualization. The position of a tubular working channel is confirmed by fluoroscopic guidance, and serial dilators (METRx™ lumbar endoscopic system, Medtronic) are used to dilate the musculature and expand the fascia. For MEDL, an endoscopic curette, rongeur, and drill are used for the laminotomy, facetectomy, and foraminotomy. The working channel may be repositioned from a single incision for multilevel and bilateral dissections.
Minimally invasive procedures in nerve and/or soft tissue such as the spine or the breast, however, are difficult to perform using standard scissors and scalpel. Therefore, methods of cutting tissue may include using a scalpel and scissors or electrosurgical procedures using radio frequency (RF) energy. Electrosurgical procedures and techniques using radio frequency energy are currently used since they generally reduce patient bleeding and trauma associated with cutting operations.
Radio frequency energy controls bleeding by coagulating small blood vessels. Another method of controlling bleeding is through the use of heat. For example, some commercially available scalpels use direct heat to control bleeding. However, while the bleeding is generally controlled, the cutting of tissue is often slower than with radio frequency energy and the knife edge readily dulls. Other commercially available scalpels use ultrasonic energy generally at 50 kHz to heat the tissue so as to coagulate severed blood vessels but cut slower than a standard electrosurgical electrode and are costly as a custom ultrasonic generator is required.
Radiofrequency energy is used in a wide range of surgical procedures because it provides efficient tissue resection and coagulation and relatively easy access to the target tissues through a portal or cannula. Conventional monopolar high frequency electrosurgical devices typically operate by creating a voltage difference between the active electrode and the target tissue, causing an electrical arc to form across the physical gap between the electrode and tissue. At the point of contact of the electric arcs with tissue, rapid tissue heating occurs due to high current density between the electrode and tissue. This high current density causes cellular fluids to rapidly vaporize into steam, thereby producing a “cutting effect” along the pathway of localized tissue heating. Thus, the tissue is parted along the pathway of evaporated cellular fluid, inducing undesirable collateral tissue damage in regions surrounding the target tissue site. This collateral tissue damage often causes indiscriminate destruction of tissue, resulting in the loss of the proper function of the tissue. In addition, the device does not remove any tissue directly, but rather depends on destroying a zone of tissue and allowing the body to eventually remove the destroyed tissue.
Present electrosurgical techniques used for tissue ablation may suffer from an inability to provide the ability for fine dissection of soft tissue. The distal end of electrosurgical devices is wide and flat, creating a relatively wide area of volumetric tissue removal and making fine dissections along tissue planes more difficult to achieve because of the lack of precision provided by the current tip geometries.
In addition, identification of the plane is more difficult because the large ablated area and overall size of the device tip obscures the physician's view of the surgical field. The inability to provide for fine dissection of soft tissue is a significant disadvantage in using electrosurgical techniques for tissue ablation, particularly in arthroscopic, otolaryngological, and spinal procedures. This disclosure describes an improvement over these prior art technologies.